Technical Field
Embodiments of the subject matter disclosed herein generally relate to actuated rotary valves useable in reciprocating compressors for oil and gas industry, and, more particularly, to translo-rotating valves that are opened by first translating the valve rotor away from the valve stator, and then rotating the valve rotor around a rotation axis to overlap an opening of the rotor with an opening of the stator in a fluid flow direction.
Discussion of the Background
Compressors used in oil and gas industry, have to meet industry specific requirements that take into consideration, for example, that the compressed fluid is frequently corrosive and flammable. American Petroleum Institute (API), the organization setting the recognized industry standard for equipment used in oil and gas industry has issued a document, API618, listing a complete set of minimum requirements for reciprocating compressors.
The compressors may be classified as positive displacement compressors (e.g., reciprocating, screw, or vane compressors) or dynamic compressors (e.g., centrifugal or axial compressors). In the positive displacement compressors, the gas is compressed by trapping a fixed volume of gas and then reducing that volume. In the dynamic compressors, the gas is compressed by transferring the kinetic energy from a rotating element (such as, an impeller) to the gas to be compressed by the compressor.
FIG. 1 is an illustration of a conventional dual chamber reciprocal compressor 10 used in the oil and gas industry. The fluid compression occurs in a cylinder 20. A fluid to be compressed (e.g., natural gas) is input into the cylinder 20 via an inlet 30, and, after the compression, is output via an outlet 40. The compression is a cyclical process in which the fluid is compressed due to a movement of the piston 50 along the cylinder 20, between a head end 26 and a crank end 28. In fact, the piston 50 divides the cylinder 20 in two compression chambers 22 and 24 operating in different phases of the compression cycle, the volume of compression chamber 22 being at its lowest value when the volume of the compression chamber 24 is at its highest value and vice-versa.
Suction valves 32 and 34 open to allow the fluid that is going to be compressed (i.e., having a first pressure p1) from the inlet 30 into the compression chambers 22 and 24, respectively. Discharge valves 42 and 44 open to allow the fluid that has been compressed (i.e., having a second pressure p2) to be output from the compression chambers 22 and 24, respectively, via the outlet 40. The piston 50 moves due to energy transmitted from a crankshaft 60 via a crosshead 70 and a piston rod 80.
Conventionally, the suction and the compression valves used in a reciprocating compressor are automatic valves that are switched between a close state and an open state due to a differential pressure across the valve. One source of inefficiency in the reciprocating compressor using automatic valves is due to the clearance volume, that is, a volume from which the compressed fluid cannot be evacuated. Rotary valves require less clearance volume than the automatic valves, but operate only if actuated by an external force. Rotary valves are known, for example, they have been described in U.S. Pat. No. 4,328, 831 to Wolff and U.S. Pat. No. 6,598,851 to Schiavone et al.
FIGS. 2A and 2B illustrate a conventional rotary valve 200. The valve includes a stator 210 and a rotor 220. The stator 210 and the rotor 220 are coaxial disks with openings spanning a sector of the same size around a shaft 230. The rotor 210 may be actuated to rotate around the shaft 230 from a first position (FIG. 2A) in which the rotor's opening 212 overlaps the stator's opening 222 to a second position (FIG. 2B) in which the rotor's opening 212 and the stator's opening 222 (shown using dashed line) span different sectors. When the rotor 220 is in the first position, the rotary valve 200 is in the open state allowing a fluid to flow from one side of the rotor stator area to another side of the rotor. When the rotor 220 is in the second position, the rotary valve 200 is in the close state preventing the fluid to flow from one side of the rotor stator area to another side of the rotor.
Rotary valves in reciprocating compressors have not been used for the oil and gas industry because a reliable seal between the stator and the rotor together and the required fast actuation times are not available. Moreover, when actuating the rotor, high friction forces may occur due to (1) the system pressure pushing the rotor towards the stator, and (2) the large friction surface.
Accordingly, it would be desirable to provide systems and methods that avoid the afore-described problems and drawbacks.